Referring to FIGS. 1 and 2, Taiwanese Invention Patent No. I350354 discloses a conventional sensor faucet adapted for mounting to a panel 3 of a sink. The sensor faucet includes a fixing unit 1 and a valve unit 2 disposed on the fixing unit 1. The fixing unit 1 includes a fixing seat 101 disposed on a top surface of the panel 3, a lower plate 102 disposed on a bottom surface of the panel 3, a bolt member 103, a nut member 104 engaged with the bolt member 103, a positioning plate 105, and two screw members 106. The bolt member 103 extends through the positioning plate 105 and the lower plate 102, and is bolted to the fixing seat 101. The screw members 106 are screwed to the positioning plate 105 and abut against the lower plate 102. The lower plate 102 and the fixing seat 101 are respectively abutted against the bottom and top surfaces of the panel 3 by the screw members 106 and the bolt member 103.
However, it is difficult to align the fixing seat 101 and the lower plate 102 with the plate 3 in between. Moreover, the user needs to be under the panel 3 (and thus under the sink) in order to tighten the bolt member 103 and the screw members 106. Space is usually limited under the sink, making it inconvenient for the user to operate tools on the bolt member 103 and the screw members 106.